"Anapji Pond was built during the 14th year of King Munmu (in power 661-681 AD) of the Silla Kingdom (57 BC-935 AD). The pond was originally built in Wolseung Fortress (erected in 101 AD during the Silla period), but the fortress was destroyed and now lies in ruins. In 1974, an excavation project revealed large spherical shapes (measuring 200 meters in diameter and 180 meters in height) which indicated that 3 islands had been located in the pond"
[source : visit Korea]